Getting a null pointer exception on a number picker - Android

Question

I am trying to do a simple "number picker" function that was custom made (not using the NumberPicker widget), by aligning 3 of them side by side. I got one to work just fine, but as soon as I added the other 2, then tried to change variable names (and adjusted it in the MainActivity), the program crashed with a NullPointer Exception. It is saying line 29 is the culprit (caused by) in the MainActivity.

I probably don't understand the MainActivity code very well, as it was code I borrowed. Why is it crashing? Thanks.

MainActivity.java

package com.azurespot.numbpicksample;

import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.app.Activity;

public class MainActivity extends Activity implements OnClickListener {
    Button btnUp, btnDown;
    TextView textViewUp, textViewMid, textViewBottom;

    int nStart = 0;
    int nEnd = 59;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnUp = (Button) findViewById(R.id.buttonUp1|R.id.buttonUp2|R.id.buttonUp3);
        btnDown = (Button) findViewById(R.id.buttonDown1|R.id.buttonDown2|R.id.buttonDown3);

        // All the numbers
        textViewUp = (TextView) findViewById(R.id.plus1|R.id.plus2|R.id.plus3);
        textViewMid = (TextView) findViewById(R.id.mainNumber1|R.id.mainNumber2|R.id.mainNumber3);
        textViewBottom = (TextView) findViewById(R.id.minus1|R.id.minus2|R.id.minus3);

        textViewUp.setText("1"); // Line 29
        textViewMid.setText("0");
        textViewBottom.setText("59");

        btnUp.setOnClickListener(this);
        btnDown.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        String getString = String.valueOf(textViewMid.getText());
        int current = Integer.parseInt(getString);
        if (v == btnUp) {
            if (current < nEnd) {
                current++;
                textViewUp.setText(String.valueOf(current - 1));
                textViewMid.setText(String.valueOf(current));
                textViewBottom.setText(String.valueOf(current + 1));
            }

        }
        if (v == btnDown) {
            if (current > nStart) {
                current--;
                textViewUp.setText(String.valueOf(current - 1));
                textViewMid.setText(String.valueOf(current));
                textViewBottom.setText(String.valueOf(current + 1));
            }
        }
    }
}

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="horizontal" >

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="left"
        android:orientation="vertical" >

        <Button
            android:id="@+id/buttonUp1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:background="@drawable/up_btn" />

        <TextView
            android:id="@+id/plus1"
            android:layout_width="43dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="plus"
            android:textColor="#cc8400"
            android:textSize="16sp" />

        <View
            android:id="@+id/topBar1"
            android:layout_width="30dp"
            android:layout_height="1dp"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:layout_marginTop="10dp"
            android:background="#000000" />

        <TextView
            android:id="@+id/mainNumber1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="Main"
            android:textColor="#000000"
            android:textSize="30sp" />

        <View
            android:id="@+id/lowerBar1"
            android:layout_width="30dp"
            android:layout_height="1dp"
            android:layout_marginBottom="5dp"
            android:layout_gravity="center_horizontal"
            android:background="#000000" />

        <TextView
            android:id="@+id/minus1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="minus"
            android:textColor="#cc8400"
            android:textSize="16sp" />

        <Button
            android:id="@+id/buttonDown1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:background="@drawable/down_btn" />

    </LinearLayout>

<!-- start center numberpicker -->

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:orientation="vertical" >

        <Button
            android:id="@+id/buttonUp2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:background="@drawable/up_btn" />

        <TextView
            android:id="@+id/plus2"
            android:layout_width="43dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="plus"
            android:textColor="#cc8400"
            android:textSize="16sp" />

        <View
            android:id="@+id/topBar2"
            android:layout_width="30dp"
            android:layout_height="1dp"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:layout_marginTop="10dp"
            android:background="#000000" />

        <TextView
            android:id="@+id/mainNumber2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="Main"
            android:textColor="#000000"
            android:textSize="30sp" />

        <View
            android:id="@+id/lowerBar2"
            android:layout_width="30dp"
            android:layout_height="1dp"
            android:layout_marginBottom="5dp"
            android:layout_gravity="center_horizontal"
            android:background="#000000" />

        <TextView
            android:id="@+id/minus2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="minus"
            android:textColor="#cc8400"
            android:textSize="16sp" />

        <Button
            android:id="@+id/buttonDown2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:background="@drawable/down_btn" />

    </LinearLayout>

    <!-- start right numberpicker -->

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:orientation="vertical" >

        <Button
            android:id="@+id/buttonUp3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:background="@drawable/up_btn" />

        <TextView
            android:id="@+id/plus3"
            android:layout_width="43dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="plus"
            android:textColor="#cc8400"
            android:textSize="16sp" />

        <View
            android:id="@+id/topBar3"
            android:layout_width="30dp"
            android:layout_height="1dp"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:layout_marginTop="10dp"
            android:background="#000000" />

        <TextView
            android:id="@+id/mainNumber3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="Main"
            android:textColor="#000000"
            android:textSize="30sp" />

        <View
            android:id="@+id/lowerBar3"
            android:layout_width="30dp"
            android:layout_height="1dp"
            android:layout_marginBottom="5dp"
            android:layout_gravity="center_horizontal"
            android:background="#000000" />

        <TextView
            android:id="@+id/minus3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:layout_marginBottom="5dp"
            android:text="minus"
            android:textColor="#cc8400"
            android:textSize="16sp" />

        <Button
            android:id="@+id/buttonDown3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:background="@drawable/down_btn" />

    </LinearLayout>

</LinearLayout>

LogCat

FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.azurespot.numbpicksample/com.azurespot.numbpicksample.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5041)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.azurespot.numbpicksample.MainActivity.onCreate(MainActivity.java:29)
            at android.app.Activity.performCreate(Activity.java:5104)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5041)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)

Answer 1

You cant use | to separate layout variables while initialising..

So replace this

btnUp = (Button) findViewById(R.id.buttonUp1|R.id.buttonUp2|R.id.buttonUp3); 

as

 btnUp = (Button) findViewById(R.id.buttonUp1);

Similarly do it for others also..

Answer 2

You can find the id of every view in your R.java file. And thats auto generated(can't be changed) and unique. The syntax allows you to use OR. Because the result will be an int. But there might be no view with the id of the result R.id.buttonUp1|R.id.buttonUp2|R.id.buttonUp3. Thats the reason for the NPE

Answer 3

// try this way,hope this will help you...

public class MainActivity extends Activity implements View.OnClickListener {
    Button buttonUp1;
    Button buttonUp2;
    Button buttonUp3;
    Button buttonDown1;
    Button buttonDown2;
    Button buttonDown3;
    TextView mainNumber1;
    TextView mainNumber2;
    TextView mainNumber3;
    TextView plus1;
    TextView plus2;
    TextView plus3;
    TextView minus1;
    TextView minus2;
    TextView minus3;


    int nStart = 0;
    int nEnd = 59;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        buttonUp1 = (Button) findViewById(R.id.buttonUp1);
        buttonUp2 = (Button) findViewById(R.id.buttonUp2);
        buttonUp3 = (Button) findViewById(R.id.buttonUp3);
        buttonDown1 = (Button) findViewById(R.id.buttonDown1);
        buttonDown2 = (Button) findViewById(R.id.buttonDown2);
        buttonDown3 = (Button) findViewById(R.id.buttonDown3);


        // All the numbers
        mainNumber1 = (TextView) findViewById(R.id.mainNumber1);
        mainNumber2 = (TextView) findViewById(R.id.mainNumber2);
        mainNumber3 = (TextView) findViewById(R.id.mainNumber3);
        plus1 = (TextView) findViewById(R.id.plus1);
        plus2 = (TextView) findViewById(R.id.plus2);
        plus3 = (TextView) findViewById(R.id.plus3);
        minus1 = (TextView) findViewById(R.id.minus1);
        minus2 = (TextView) findViewById(R.id.minus2);
        minus3 = (TextView) findViewById(R.id.minus3);


        plus1.setText("1");
        plus2.setText("1");
        plus3.setText("1");
        minus1.setText("59");
        minus2.setText("59");
        minus3.setText("59");
        mainNumber1.setText("0");
        mainNumber2.setText("0");
        mainNumber3.setText("0");

        buttonUp1.setOnClickListener(this);
        buttonUp2.setOnClickListener(this);
        buttonUp3.setOnClickListener(this);
        buttonDown1.setOnClickListener(this);
        buttonDown2.setOnClickListener(this);
        buttonDown3.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.buttonUp1 :
                int upp1 = Integer.parseInt(plus1.getText().toString());
                int upm1 = Integer.parseInt(mainNumber1.getText().toString());
                int upd1 = Integer.parseInt(minus1.getText().toString());
                if (upm1 < nEnd) {
                    upm1++;
                    plus1.setText(String.valueOf(upp1 + 1));
                    mainNumber1.setText(String.valueOf(upm1));
                    minus1.setText(String.valueOf(upd1 - 1));
                }
            break;
            case R.id.buttonUp2 :
                int upp2 = Integer.parseInt(plus2.getText().toString());
                int upm2 = Integer.parseInt(mainNumber2.getText().toString());
                int upd2 = Integer.parseInt(minus2.getText().toString());
                if (upm2 < nEnd) {
                    upm2++;
                    plus2.setText(String.valueOf(upp2 + 1));
                    mainNumber2.setText(String.valueOf(upm2));
                    minus2.setText(String.valueOf(upd2 - 1));
                }
                break;
            case R.id.buttonUp3 :
                int upp3 = Integer.parseInt(plus3.getText().toString());
                int upm3 = Integer.parseInt(mainNumber3.getText().toString());
                int upd3 = Integer.parseInt(minus3.getText().toString());
                if (upm3 < nEnd) {
                    upm3++;
                    plus3.setText(String.valueOf(upp3 + 1));
                    mainNumber3.setText(String.valueOf(upm3));
                    minus3.setText(String.valueOf(upd3 - 1));
                }
                break;
            case R.id.buttonDown1 :
                int downp1 = Integer.parseInt(plus1.getText().toString());
                int downm1 = Integer.parseInt(mainNumber1.getText().toString());
                int downd1 = Integer.parseInt(minus1.getText().toString());
                if (downm1 > nStart) {
                    downm1--;
                    plus1.setText(String.valueOf(downp1 - 1));
                    mainNumber1.setText(String.valueOf(downm1));
                    minus1.setText(String.valueOf(downd1 + 1));
                }
                break;
            case R.id.buttonDown2 :
                int downp2 = Integer.parseInt(plus2.getText().toString());
                int downm2 = Integer.parseInt(mainNumber2.getText().toString());
                int downd2 = Integer.parseInt(minus2.getText().toString());
                if (downm2 > nStart) {
                    downm2--;
                    plus2.setText(String.valueOf(downp2 - 1));
                    mainNumber2.setText(String.valueOf(downm2));
                    minus2.setText(String.valueOf(downd2 + 1));
                }
                break;
            case R.id.buttonDown3 :
                int downp3 = Integer.parseInt(plus3.getText().toString());
                int downm3 = Integer.parseInt(mainNumber3.getText().toString());
                int downd3 = Integer.parseInt(minus3.getText().toString());
                if (downm3 > nStart) {
                    downm3--;
                    plus3.setText(String.valueOf(downp3 - 1));
                    mainNumber3.setText(String.valueOf(downm3));
                    minus3.setText(String.valueOf(downd3 + 1));
                }
                break;
        }
    }
}